Fig. 1.

(A) Schematic layout of the DFXM experiment. The incident X-ray beam is condensed in one direction using a compound refractive lens (CRL) to illuminate a layer in the sample, which defines the observation plane (horizontal in this figure). The diamond single crystal is oriented such that diffraction takes place on reflection, $\overrightarrow{Q}$  . DFXM images of the observation plane are obtained by using an X-ray objective to magnify the Bragg diffracted X-rays onto a 2D detector. An optical laser pump heats a Au film deposited on the surface of the sample at time t₀, leading to thermal expansion and the launching of acoustic waves inside the diamond crystal. The associated local strain variations in the crystalline lattice are imaged at different time delays Δt between the laser pump and X-ray probe to create a movie of their propagation. Facets of the crystal and a laboratory coordinate system are shown. (B) Scattering geometry. (C) Experimental DFXM images at Δt = 3 ns and 7 ns. Below are graphs of intensity with the vertical y_ℓ-direction integrated out. Two acoustic waves, marked A₀ (aquamarine) and B₀ (blue), are seen to propagate toward the right for increasing Δt.